Experimental study on dynamic mechanical properties and damage mechanisms models of concrete under freeze-thaw cycles.

Freeze-thaw (F-T) cycles represent a major driver of concrete deterioration in cold regions, significantly compromising structural integrity. In this research, uniaxial compression tests on concrete subjected to F-T cycles at different strain rates were carried out, and an evolution model for dynamic mechanical properties was developed to clarify the associated degradation mechanisms. Results show that F-T cycles reduce compressive strength and elastic modulus while concurrently increasing residual and peak strains. The strain rate sensitivity of compressive strength, peak strain, and elastic modulus progressively increased with the number of F-T cycles, whereas the sensitivity of compressive strength and peak strain to initial F-T damage decreased at higher strain rates. The peak of the compressive stress-strain curves at various strain rates significantly decreased and shifted backward with increasing F-T cycles, indicating that F-T action reduces the energy absorption capacity. Additionally, the ductility of concrete with initial F-T damage increased, an effect more pronounced at lower strain rates.The surface fracture density, width, and quantity increased with F-T cycles, and fracture patterns transitioned from localized fracture failure to bulging failure as F-T cycles progressed. These findings provide a theoretical framework for assessing the long-term performance and predicting the service life of hydraulic concrete structures in cold regions.